Proteins

Question 1

What are proteins?

Answer 1

Proteins are biomolecules made of amino acids joined by peptide bonds via condensation reactions.

Question 2

Protein denaturation

Answer 2

Denaturation is a structural change in a protein causing loss of function.
Caused by:

High temperature (breaks bonds via vibration)

pH extremes (H⁺ or OH⁻ disrupt ionic/R-group bonds)
If primary structure is intact, denaturation may be reversible.

Question 2

What is a condensation reaction?

Answer 2

A reaction where a water molecule is removed, and a peptide bond forms between two amino acids → forms dipeptides or polypeptides.

Question 3

Temperature and Denaturation

Answer 3

Increased kinetic energy breaks intermolecular bonds (e.g. hydrogen bonds), changing the protein’s 3D shape → loses function.

Question 4

pH and Denaturation

Answer 4

Acidic or alkaline pH introduces H⁺ or OH⁻, interfering with ionic interactions in R-groups → breaks structure → denaturation.

Question 5

Types of Amino Acids

Answer 5

Essential: Must come from diet

Conditionally essential: e.g. Tyrosine (from phenylalanine); Arginine (infants can’t make it)

Non-essential: Synthesized in body from other amino acids

Question 6

8. Infinite polypeptide diversity – Why?

Answer 6

20 amino acids

Any sequence or length

For 7 amino acids: 20⁷ = 1.28 billion combinations

Question 7

9. DNA to Protein Overview

Answer 7

DNA → mRNA (transcription)

mRNA exits via nuclear pores

Ribosome reads codons (3 bases)

tRNA delivers amino acids using anticodons

Codon CGU = Arginine

Question 8

Insulin

Answer 8

Blood sugar regulation

Question 9

Haemoglobin

Answer 9

Oxygen transport

Question 10

Lipase

Answer 10

Lipid digestion

Question 11

Histones

Answer 11

DNA packaging

Question 11

Immunoglobulins

Answer 11

Antibodies

Question 12

Keratin

Answer 12

Hair, nails, hooves

Question 13

Collagen

Answer 13

Connective tissue

Question 14

Actin and Myosin

Answer 14

Muscle movement

Question 15

What determines protein structure?

Answer 15

Primary structure (amino acid sequence) → determines R-group interactions → shapes secondary, tertiary, and quaternary structures.

Question 16

Secondary Structure

Answer 16

Alpha helix: Coiled shape

Beta-pleated sheet: Zigzag pattern

Stabilized by H-bonds between non-adjacent amine and carboxyl groups

Question 17

Tertiary Structure

Answer 17

D folding from R-group interactions:

Hydrogen bonds

Ionic bonds

Disulfide bridges (cysteine–cysteine)

Hydrophobic interactions

Polar associations

Question 18

Quaternary Structure

Answer 18

Formed by interaction of multiple polypeptide chains

May include prosthetic groups
→ e.g. Haem in haemoglobin

Example proteins: Haemoglobin, Collagen, Insulin

Question 19

What are prosthetic groups?

Answer 19

Non-protein (often inorganic) groups that aid structure or function
E.g., heme group in haemoglobin
→ proteins with prosthetic groups = conjugated proteins

Question 19

Fibrous vs Globular Proteins

Answer 19

Fibrous: Long, narrow, structural (e.g. Collagen, Keratin)

Globular: Compact, round, functional (e.g. Insulin, Enzymes)

Question 20

Why insulin is globular?

Answer 20

Compact & soluble in blood

Has a quaternary shape

Binds to specific receptors on cell membranes

Triggers glucose uptake

Question 20

Why collagen is fibrous?

Answer 20

riple helix structure → forms fibers

Found in bones, ligaments, tendons, cartilage

Strong, flexible, not soluble in water

Question 21

Why is haemoglobin a conjugated protein?

Answer 21

Has 4 polypeptide chains (quaternary) Each chain includes a heme group (prosthetic group) Binds and carries oxygen

Question 22

Hydrophobic vs Hydrophilic Amino Acids

Answer 22

Hydrophobic R-groups cluster inside proteins in water Hydrophilic R-groups face outside Enables proteins to be soluble or membrane-embedded

Question 23

Integral membrane proteins

Answer 23

Hydrophobic regions embedded in membrane core Hydrophilic regions face cytoplasm or extracellular fluid